;画磁力线
theta=[-!PI:!PI:!PI/50.]
RE=1.
L=findgen(5)*0.6+0.6
foreach i,L do p=polarplot(i*RE*sin(theta)*sin(theta),theta,color='blue',/overplot,thick=2.)
p=polarplot(RE+fltarr(size(theta,/n_elements)),theta,color='red',/overplot)
p.xrange=[-max(L)*RE,max(L)*RE]
p.yrange=p.xrange
p.thick=2
p.save, '../docs/mag_line.eps'
end